1. Field of the Invention
The present invention relates to a vehicle steering device in which a steering operation mechanism is driven by a steering motor with a steering member to be operated for steering operation and the steering operation mechanism are not mechanically coupled to each other.
2. Description of Related Art
There is proposed a steer-by-wire system in which the drive force of a steering motor to be controlled in accordance with an operation of a steering wheel that serves as a steering member is transferred to a steering operation mechanism with the steering wheel and the steering operation mechanism not mechanically coupled to each other. Such a steer-by-wire system includes a reaction force motor that applies a reaction force to the steering wheel. An input shaft is coupled to the steering wheel. An output shaft is coupled to the reaction force motor. The input shaft and the output shaft are coupled to each other by a torsion bar so as to be relatively rotatable. See Japanese Patent Application Publication No. 2006-240399 (JP 2006-240399 A), for example.
In the steer-by-wire system discussed earlier, it is conceivable to set a target rotational angle which is a target value for the rotational angle of the output shaft, and to control the reaction force motor such that the rotational angle of the output shaft is equal to the target rotational angle. It is also conceivable to control the reaction force motor such that the steering wheel is not rotated any further, by temporarily fixing the target rotational angle for the output shaft, when the steered angle of steered wheels has reached a steered angle limit value. Even if the target rotational angle for the output shaft is temporarily fixed, however, the torsion bar may be twisted by steering torque to rotate the steering wheel.